The present invention relates to slip systems useful for anchoring devices to downhole surfaces found in open wellbores or casing pipe. More particularly, the invention relates to a high expansion slip system which is expandable from a narrow profile to engage a downhole surface.
Compression slip devices anchor wellbore tools to open wellbores and to the interior wall of casing set within a wellbore. Conventional wellbore tools using slip devices include packers, plugs and straddles. Slip devices are constructed in many different configurations, including cone types, dovetails, collets, wedges, C-rings, and other known devices. These conventional slip devices may also use a retainer device such as a cage, slip ring, pocket, fracturable ring, collet or other device.
Slip design is typically integrated into the wellbore tool cooperating with the slips system. For a packer, a cylindrical packer body typically provides a chassis for containing the packer element, a slip system, and for containing the interior pressure within the packer body interior. The packer element has an outside diameter greater than the outside diameter of the packer body as the packer is lowered into a wellbore, and the radial difference between these two diameters is defined as "annular thickness". Conventional slip systems fit within this annular thickness so that the exterior dimension is insertable into the wellbore, and so that the interior dimension does not interfere with fluid flow and tool movement through the system. Multiple stair-stepped cones have been proposed to expand the effective radial reach of a backup ring system, however such systems are complex and do not have a high degree of reliability.
One form of high expansion, through-tubing slip system was disclosed in U.S. Pat. No. 3,706,342 to Woolley (1972). Woolley disclosed a seal element positioned about a cylinder which was expanded by an overlapping system of mechanical fingers. After the apparatus was lowered through a well tubing, two opposing sets of fingers were drawn together to compress and radially expand a packing element. As in other conventional slip systems, the interior dimension available for fluid flow and tool movement was limited to the interior body dimension of the tool mandrel.